Microdetermination of Proteins by Enhanced Rayleigh Light Scattering Spectroscopy with Thorin

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Spectrophotometric determination of trace level thorium with n-phenylbenzohydroxamic acid

A method for the determination of thorium(IV) based on thorium-PBHA complex, which is extracted into amyl alcohol, is described. The thorium is back-extracted from amyl alcohol with 0.2M hydrochloric acid and estimated spectrophotometrically with thorin. The system has a maximum absorbance at 545 nm and obeys Beer's law between 0.5 to 12.5 ppm and the molar absorption coefficients is 1.7·10 1·mol^?1·cm^?1., Various parameters for the extraction and back-extraction and the effect of diverse ions have been studied.     

Spectroscopic studies of the reaction of iodine with the mixed oxygen—nitrogen cyclic base 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane

The reaction of iodine with the interesting mixed oxygen—nitrogen cyclic base 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (TODACOD) has been investigated spectrophotometrically in the solvent 1,2-dichloroethane. The spectra indicate the formation of the pentaiodide ion, I⁻₅, judging from its two strong absorptions around 360 and 290 nm. Elemental analysis for the solid iodine—(TODACOD) complex indicate that the (TODACOD) base—iodine ratio is 1:3 in agreement with the ratio concluded from the photometric titration plots based on the absorptions of the formed polyiodide ion. Therefore, the formed iodine complex is formulated as [(TODACOD)I]⁺.I⁻₅. The formation of the I⁻₅ species was also confirmed by the resonance Raman spectrum of the solid product. The Raman spectrum can be explained entirely by the presence of the bent I⁻₅ ion with C_2υ structure. The vibrations of I⁻₅ ion are ν_s(II); outer, ν_s(II); inner, ν_as(II); outer, and ν_as(II); inner and are assigned as expected at 164, 110, 137 and 87 cm⁻¹, respectively.     

Determination of ceftriaxone by the fluorescence quenching of quantum dots using binding with polyethyleneimine

It is found that antibiotic ceftriaxone reacts with polyethyleneimine in aqueous solutions, probably, with the formation of a noncovalent molecular complex (complex I). The product of hydrolysis of complex I, when heated in an aqueous solution (product II), quenches the fluorescence of CdSe/CdS/ZnS coreshell- shell quantum dots, probably, because of the formation of free thiol groups. A possibility of ceftriaxone determination in aqueous solutions is demonstrated. The performance characteristics of the procedure using a spectrofluorimeter and a photocamera combined with a UV light-emitting diode are close to each other (cmin = 1 × 10^–6 M, RSD = 10%). Na⁺, Ca²⁺, glucose, urea, uric acid, erythromycin, ciprofloxacin, and doxycycline produce no analytical signals under the conditions of ceftriaxone determination.     

Spectrophotometric determination of microamounts of thorium with thorin in the presence of cetylpyridinium chloride as surfactant in perchloric acid

A simple and more sensitive spectrophotometric method is developed for determination of thorium using thorin as a chromogenic reagent in the presence of cetylpyridinium chloride (CPC) in perchloric acid. The reaction was instantaneous and complex was found stable for 168 h. A significant bathochromic shift was noted in the presence of CPC. The determination range was enhanced from 25 to 30 μg mL^?1 with molar absorptivity of 2.95 × 104 L mol^?1 cm^?1 at 25 ± 5 °C. Sandell’s sensitivity was calculated to be 6.8 ng cm^?2 at 581 nm. Relative standard deviation was reduced from 4.25 to 2.5. The interference of Ni²⁺, Mn²⁺, Sn⁴⁺, phosphate, EDTA, sulphate and tartrate has been reduced significantly in the presence of surfactant. The validity of the proposed method was tested by determining thorium in Certified Reference Materials.     

Removal of interferences in absorptiometric determination of bismuth with thorin

Bismuth can be separated by ion-exchange adsorption on Dowex 21 K resin from ca. 0.25 M HCl, after removal of volatile interferences by distillation in acid-oxidizing medium. Bismuth is eluted from the column with 1 M sulfuric acid. The method is useful in the absorptiometric determination of bismuth with thorin, as well as in other photometric methods.     

Batch and flow-injection determination of ethylenediamine in pharmaceutical preparations

the ethylenediamine/pyridine-2-carbaldehyde/copper(I) system is used in a new spectrophotometric method for the determination of ethylenediamine. The batch procedure involves the formation of an orange chelate between the Schiff's base and copper(I) ions at pH 8.5 (borate buffer) and measurement of the absorbances at 475 nm against water after 10/2-15 min; Beer's law is obeyed over the range 0.5/2-11.2 μg ml^?1 and the molar absorptivity is 6.21 × 10³ l mol^?1 cm^?1. Tolerance limits for different amines [36] and other organic compounds [12] are reported. In the optimized flow-injection system, ethylenediamine (1.4/2-84.6 μg ml^?1 is determined at a sample throughput of 55 h^?1. The method is sensitive and selective and is satisfactory for the determination of the diamine in aminophylline and pharmaceutical preparations (ethylenediamine contents from 0.031 to 3.23%) with relative errors ranging from ?7.4 to +11.1% and relative standard deviations of about 0.65% for both procedures.     

Two Distinct Thermal Stabilities of DNA and Enzymatic Activities of DNase I in a Multistep Assembly with Carbazole Ligands: Different Binding Characteristics for Duplex and Quadruplex DNA

A partially hydrophobic carbazole ligand ((Im⁺)₂Cz: 2,2′‐(9‐ethyl‐9 H‐carbazole‐3,6‐diyl)bis(ethyne‐2,1‐diyl)bis(1,3‐dimethyl‐1 H‐imidazol‐3‐ium)) adopts two different binding states (binding states I and II) in its interactions with calf‐thymus (ct‐) DNA. Two distinct binding states were identified by biphasic UV/Vis and circular dichroism (CD) spectral changes during the titration of DNA into the carbazole ligand. At low concentrations of ct‐DNA, (Im⁺)₂Cz binds to nearly every part of ct‐DNA (binding state I). By contrast, an increased concentration of ct‐DNA results in a switch in the DNA‐binding state, so that the ligands are bound per five DNA base pairs. Similarly, a monocationic carbazole ligand (Im⁺Cz: 2‐((6‐bromo‐9‐ethyl‐9 H‐carbazol‐3‐yl)ethynyl)‐1,3‐dimethyl‐1 H‐imidazol‐3‐ium) also shows biphasic UV/Vis spectral changes during the titration of ct‐DNA into Im⁺Cz, which suggests two different binding states of the Im⁺Cz ligand with ct‐DNA. The stepwise equilibrium of the ligand–DNA‐complex formation is capable of switching the thermal stability of ct‐DNA, as well as the enzymatic activity of deoxyribonuclease (DNase I). In binding state I, the (Im⁺)₂Cz ligands interact with nearly every base pair in ct‐DNA and stabilize the double‐helix structure, which results in a larger increase in the melting temperature of the ct‐DNA than that observed with binding state II. On the other hand, the (Im⁺)₂Cz ligand significantly reduces the enzymatic activity of DNase I in binding state I, although the enzymatic activity is recovered once the binding state of the ligand–DNA complex is changed to binding state II. The (Im⁺)₂Cz ligand was also employed as a binder for G‐quadruplex DNA. In contrast to the stepwise complex formation between (Im⁺)₂Cz and ct‐DNA, (Im⁺)₂Cz shows a monotonous UV/Vis spectral response during the titration of G‐quadruplex DNA into (Im⁺)₂Cz, which suggests a single binding state for (Im⁺)₂Cz with G‐quadruplex DNA.     

Photophysical characteristics and density functional theory calculations of indole 2-carboxylic acid in the presence of mercurous ions

Many photo-physical studies have been reported for the detection of Hg²⁺ ions. Here we present the effect of Hg ₂ ²⁺ ions on the absorption and fluorescence of indole-2-carboxylic acid (I2C). Experimental evidence, supported by density functional theory B3LYP/LANL2DZ/PCM, for the formation of a I2C-Hg ₂ ²⁺ complex, is reported for the first time. It was observed that I2C forms a ground-state complex with Hg ₂ ²⁺ ions in a ratio of 3:1. The possibility of I2C to be used as a selective novel chemical sensor for the spectrophotometric detection of mercurous ions is described.     

Highly Stable Double‐Stranded DNA Containing Sequential Silver(I)‐Mediated 7‐Deazaadenine/Thymine Watson–Crick Base Pairs

The oligonucleotide d(TX)₉, which consists of an octadecamer sequence with alternating non‐canonical 7‐deazaadenine (X) and canonical thymine (T) as the nucleobases, was synthesized and shown to hybridize into double‐stranded DNA through the formation of hydrogen‐bonded Watson–Crick base pairs. dsDNA with metal‐mediated base pairs was then obtained by selectively replacing W‐C hydrogen bonds by coordination bonds to central silver(I) ions. The oligonucleotide I adopts a duplex structure in the absence of Ag⁺ ions, and its stability is significantly enhanced in the presence of Ag⁺ ions while its double‐helix structure is retained. Temperature‐dependent UV spectroscopy, circular dichroism spectroscopy, and ESI mass spectrometry were used to confirm the selective formation of the silver(I)‐mediated base pairs. This strategy could become useful for preparing stable metallo‐DNA‐based nanostructures.     

The Template Synthesis of the New Macrocyclic and Acyclic Metal Ion Complexes Derived from Putrescine

The template reaction of 2,6-diacetylpyridine with biogenic diamine–putrescine in the presence of cadmium(II), mercury(II) or lead(II) ions produces the complexes of 22-membered macrocyclic ligand L¹ with an N₆ set of donor atoms as a result of [2 + 2] Schiff base cyclocondensation. The lead(II) complex containing Schiff base acyclic ligand L² terminated by one carbonyl and one amine group as product of the partial [2 + 2] condensation has been also isolated and might be regarded as possible intermediate in the formation of the macrocyclic L¹ complex. Analogous reaction involving the uranyl nitrate generates the complex containing the same Schiff base acyclic ligand L² as a final product of template reaction. The complexes were characterized by spectral data (IR, ¹H NMR, FAB-MS), thermogravimetric and elemental analyses. A notable feature of the FAB mass spectrum of the uranyl complex is the appearance of the clusters of the form [(UO₂) _n O]⁺(n= 1–7) along with the peak corresponding to molecular ion.     

Spectrophotometric determination of microamounts of thorium with disodium salt of 2-(2-hydroxy-3,6-disulfo-1-naphthylazo)-benzenearsonic acid (Thorin) as a chromogenic reagent

A sensitive spectrophotometric method has been developed for the determination of microamounts of thorium using 0.05% thorin in a 3M perchloric acid solution as a chromogenic reagent and measuring the absorbance at 544 nm. The complex of thorium thus formed, is stable for more than two months with a constant absorbance of ±0.55%. Beer's law is obeyed from 0 to 25 g g^–1 of thorium in a solution with a molar absorptivity (544 nm) = 1.69×10⁴ M^–1 cm^–1 at 26±1 °C. Among the anions tested, only phosphate, acetate and cyanide at >200-fold excess of thorium interfere in the determination, whereas cations like Zn(II), Al(III), Na(I), Mg(II), and Ca(II) do not effect the absorbance. Thorium can be determined in the presence of oxalate, nitrate, tartrate, sulfate, thiosulfate, citrate, and ascorbate. The accuracy of the method has been checked by measuring the known concentration of thorium in the range of 100 g-5 mg g^–1 and found to be in the range of 7.7–0.9%. The method has been applied successfully to determine thorium at g g^–1 level in local ore samples with a precision of ±0.3%. The sensitivity of the method on Sandell's scale is 0.082±0.002 g g^–1 cm^–1.     

Donor ligand, basal ligand and solvent effects on the equilibrium constants of triphenylphosphinecobalt(III) Schiff base complexes with phosphite ligands

The equilibrium constants and the thermodynamic parameters were spectrophotometrically measured for the 1:1 adduct formation of [Co(Salen)(PPh₃)]ClO₄.H₂O, and [Co(7,7′-Me₂Salen)(PPh₃)]ClO₄.H₂O as acceptors, with P(OR)₃ (R = methyl, ethyl, and i-propyl) as donors, in acetonitrile (CH₃CN) and dimethylformamide (DMF) as solvents at constant ionic strength (I = 0.1 M NaClO₄), and various temperatures (t = 10–50 °C). Our results revealed the following trends: stability of the cobalt(III) Schiff base complexes toward a given phosphite donor, [Co(7,7′-Me₂Salen)(PPh₃)]⁺ < [Co(Salen)(PPh₃)]⁺; binding of the donors (phosphites) toward a given cobalt(III) Schiff base complex, P(OEt)₃ > P(OMe)₃ > P(O-ⁱPr)₃; influence of solvent on the stability of a given cobalt(III) Schiff base complex toward a given phosphite donor, CH₃CN < DMF.     

Transformation of glutaryl chloride to 4,5-dibromopentanoic acid in the presence of a saturated hydrocarbon as a reducing agent and AlBr3 as the brominating agent

Conclusions Glutaryl chloride in the complex, ClCO(CH₂)₃COCl·4AlBr₃, reacts with normal alkanes and cycloalkanes with the formation of 4,5-dibromopentanoic acid after hydrolysis.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1170–1173, May, 1989.The authors express their gratitude to V. I. Dostovalova for a discussion of the PMR and¹³C NMR spectra.     

Reversible formation of binuclear complexes between pyridine-2-carboxylato(tetraethylenepentamine)cobalt(III) and nickel(II)/cobalt(II) in aqueous solution. Anomalous behaviour in the dissociation of binuclear complexes

The kinetics of the reversible formation of binuclear species between M(OH₂) ₆ ²⁺ (M = Ni^II and Co^II) and oxygen-bonded (tetren)Co(pycH)³⁺ (tetren = tetraethylenepentamine, pycH = N-protonated pyridine-2-carboxylate) have been investigated by stopped-flow spectrophotometry at 25°C, I = 0.3 mol dm^-3. Both the protonated (pyridine-N) and deprotonated forms of the Co^III complex were involved in the formation of the binuclear complex (tetren)Co(pyc)Co⁴⁺, whereas only the deprotonated form of the complex was involved in the formation of (tetren)Co(pyc)Ni⁴⁺. The rate date forthe formation of the binuclear complex are consistent with an Id mechanism. Interestingly, the dissociation of the binuclear Co^II complex (tetren)Co(pyc)Co⁴⁺ was acid-catalysed while that with Ni^II was acid-independent. A suitable explanation for this anomalous behaviour has been discussed.     

Paramagnetic nickel(I) complexes and their role in the catalytic dimerization of norbornadiene

The kinetics of the formation of a paramagnetic nickel(I) complex from bis(η³-allyl)nickel under conditions of catalytic norbornadiene dimerization is reported. It is demonstrated by ESR and GLC that the concentrations of Ni(I), norbornadiene and its pentacyclic dimers change in the same way. It might be inferred from this finding that Ni(I) is involved in the catalytic process as an intermediate. However, experiments on model systems have not confirmed this assumption. At the same time, they have not ruled out the participation of the paramagnetic complex in side catalytic reactions. The presence of Ni(I) in the reaction system is connected with the presence of free norbornadiene there. Hypotheses as to the probable structure and formation mechanism of the paramagnetic Ni(I) are suggested.     

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Results of mass spectrometric studies are reported for the collisional dissociation of Group XI (Cu, Ag, Au) metal ion complexes with fatty acids (palmitic, oleic, linoleic and α-linolenic) and glycerolipids. Remarkably, the formation of M₂H⁺ ions (M = Cu, Ag) is observed as a dissociation product of the ion complexes containing more than one metal cation and only if the lipid in the complex contains a double bond. Ag₂H⁺ is formed as the main dissociation channel for all three of the fatty acids containing double bonds that were investigated while Cu₂H⁺ is formed with one of the fatty acids and, although abundant, is not the dominant dissociation channel. Also, Cu(I) and Ag(I) ion complexes were observed with glycerolipids (including triacylglycerols and glycerophospholipids) containing either saturated or unsaturated fatty acid substituents. Interestingly, Ag₂H⁺ ion is formed in a major fragmentation channel with the lipids that are able to form the complex with two metal cations (triacylglycerols and glycerophosphoglycerols), while lipids containing a fixed positive charge (glycerophospocholines) complex only with a single metal cation. The formation of Ag₂H⁺ ion is a significant dissociation channel from the complex ion [Ag₂(L–H)]⁺ where L = Glycerophospholipid (GP) (18:1/18:1). Cu(I) also forms complexes of two metal cations with glycerophospholipids but these do not produce Cu₂H⁺ upon dissociation. Rather organic fragments, not containing Cu(I), are formed, perhaps due to different interactions of these metal cations with lipids resulting from the much smaller ionic radius of Cu(I) compared to Ag(I).     

Synthesis and reaction of Schiff base 4-(pyridin-3-ylmethylimino)-pent-2-en-2-ol with FeCl3

A potentially tridentate Schiff base 4-(pyridin-3-ylmethylimino)-pent-2-en-2-ol was synthesized in the condensation reaction of 3-picolylamine and acetylacetone. The compound was characterized by ¹H,¹³C-NMR and IR spectra. The reaction of Schiff base with Fe(III) in the acetone solution and the presence of pyridine led to its hydrolysis and the formation of the octahedral complex [Fe(acac)Cl₂(py)₂]. The structure of the complex was determined by the single crystal X-ray diffraction analysis. The magnetic properties and the molar conductivity of the complex compound were also derived.